1. Field of the Invention
The invention relates to the continuous casting of thin metal products, particularly in steel. More particularly, it relates to installations referred to as being for casting between two rolls.
2. Description of the Prior Art
It will be understand that these installations comprise two rolls with substantially horizontal, parallel and coplanar axes, rotating about their respective axes in opposite directions and having cooled lateral cylindrical surfaces forming the walls of the ingot mould against which the cast molten metal solidifies. The casting space is limited laterally by closure plates, referred to as side dams, applied against the lateral faces of the rolls. The portions of the side dams in contact with the molten metal are generally made from a refractory material with good insulating properties. The side of the side dams turned towards the rolls can be entirely flat, but it may also have a projection, or "insert", penetrating inside the inter-roll space, as in French Patent 2,636,259 in the name of the Applicant. In French Patent No. 2,636,259, the contacts between the rolls and the side dams are in the form of a wedge and it is the front face of the insert which laterally limits the casting space. The depth of penetration of this insert into the inter-roll space may be uniform over its entire height or may diminish as it descends towards the gap at the center of the rolls. The insert is then said to be recessed.
The presence of this insert is advantageous, since it permits better control of the solidification of the product in the ingot mould relative to the side dams. However, control of the play provided between each roll and the protuberant part of the insert poses a problem. In fact, it is necessary to minimise the friction between the insert and the rolls so as not to disturb the operation of the machine and, at the same time, to prevent infiltrations of molten metal between the insert and the rolls, which may occur when the play exceeds 0.1 mm. The dimensions of the insert are fixed so that the play is sufficiently small when the machine is operating under hot conditions. That is to say when the rolls which have expanded through contact with the molten steel, the rolls have reached their final radius which is increased on the order of a half millimetre relative to their size at ambient temperature. However, this expansion is not immediate: it may be spread over approximately 10 seconds from filling of the casting space. During this period of time, the play between the roll and the insert retains values which may be too large to guarantee the leaktightness of the casting space.